Millions of animals and people, especially children, are affected each year with otitis externa; i.e., infection and/or infestation of the outer ear, often accompanied by painful inflammation of the affected tissue. Animals with ear flaps, such as many breeds of dogs, are especially susceptible. Their covered outer ear canals provide an inviting environment for microbes to breed and inflammation to form, yet caretakers may not notice the condition as readily as in raised ear animals.
A variety of bacteria, viruses and fungi can be responsible for causing otits externa. Often first-line treatment is limited to oral or topical antibiotics. The use of orally administered medications may be diluted by the systemic distribution of the drug, and could place the patient at risk for side effects associated with systemic delivery (e.g., yeast infections in females). Yet the risk for fungal overgrowth in the ear canals of patients treated only with topical antibiotics for bacterial infections emphasizes a need for careful diagnosis and treatment of all the causative agents associated with otitis externa and its sequalae (Schraeder and Issacson, Pediatrics, 111(5):1123, 2003). As such, a preference is emerging for multiple agent topical treatment of otitis externa, especially in children and animals in whom compliance with a long-term oral dosing regimen can be difficult to obtain.
When single or multiple active agents are applied topically to treat otitis externa, efficacy often depends on how long the medication can be maintained in contact with the affected tissue, especially when a fungal or parasitic infestation (e.g., ear mites) is present. Conventional ear drops are problematic because the tissues they contact is directly affected by the attitude of the patient's head, and the drops can easily flow out of the ear with movement. Approaches to increasing the residence time of topical medications in the external ear canal have included use of flowable gels made more adhesive with a cellulose (e.g., hydroxypropyl methylcellulose), gel plugs, mousses, foams, or other formulations with adhesive properties.
Yet compliance with dosing regimes using such formulations is again an issue, as their thick and/or sticky feel in the ear may be a source of frustration, especially to animals and young children. If acceptance of a retainable topical formulation isn't possible, the remaining option is often more frequent, and less convenient, dosing with less viscous solutions, such as conventional ear drops. A need, therefore, exists for an approach to topical treatment of otitis externa which doesn't rely on use of gels, cellulose-based or adhesive compositions, and which can be applied infrequently (i.e., once or twice as an entire course of treatment) to ameliorate (significantly reduce symptoms) or resolve the condition.